This invention relates generally to a method and apparatus utilized in hydrocarbon exploration. More specifically the invention relates to the utilization of acoustic sources and receivers to determine acoustic properties of geologic formations as they are traversed by a logging tool, be it a wireline logging tool or a logging while drilling tool. More particularly the present invention is directed to methods and apparatus for providing acoustic isolation between an acoustic transmitter and an acoustic receiver.
Geologists and geophysicists are interested in the characteristics of the formations encountered by a drill bit as it is drilling a well for the production of hydrocarbons from the earth. Such information is useful in determining the correctness of the geophysical data used to choose the drilling location and in choosing subsequent drilling locations. In horizontal drilling, such information can be useful in determining the location of the drill bit and the direction that drilling should follow.
Such information can be derived in a number of ways. For example, cuttings from the mud returned from the drill bit location can be analyzed or a core can be bored along the entire length of the borehole. Alternatively, the drill bit can be withdrawn from the borehole and a xe2x80x9cwireline logging toolxe2x80x9d can be lowered into the borehole to take measurements. In still another approach, called xe2x80x9cmeasurement while drillingxe2x80x9d (xe2x80x9cMWDxe2x80x9d) or xe2x80x9clogging while drillingxe2x80x9d (xe2x80x9cLWDxe2x80x9d), tools make measurements in the borehole while the drill bit is working.
An acoustic logging tool collects acoustic data regarding underground formations. The purpose of such a tool is to measure the xe2x80x9cinterval transit timexe2x80x9d or the amount of time required for acoustic energy to travel a unit distance in a formation. In simple terms, this is accomplished by transmitting acoustic energy into the formation at one location and measuring the time that it takes for the acoustic energy to travel to a second location or past several locations. To improve the ability of an acoustic tool to detect the signal at the receiver, the detected signal should be effectively free of acoustic energy coupled from the transmitter to the tool body between the transmitter and the receiver and propagated to the receiver.
In general, in one aspect, the invention features an acoustic logging tool comprising an elongated body, one or more acoustic transmitters, one or more acoustic receivers, and a broadband acoustic absorption region. A substantial portion of the broadband acoustic absorption region is between the transmitter and the receiver.
In general, in another aspect, the invention features an acoustic logging tool comprising an elongated body, an acoustic transmitter, an acoustic receiver, and an acoustic energy absorber. The acoustic energy absorber comprises a first absorber for absorbing a first mode of acoustic energy and a second absorber for absorbing a second mode of acoustic energy.
Implementations of the invention may include one or more of the following. The first absorber may comprise one or more toroidal-shaped elements. The second absorber may comprise one or more elongated elements. The elongated elements may be inserted into the body. Each elongated element of the second absorber may be inserted into the body tangent to an arc centered on a longitudinal axis of the body, the arc having a radius smaller than an outside diameter of the body.
A projection of the elongated elements onto a plane perpendicular to a longitudinal axis of the body may cover between 10 and 70 percent of the cross section of the body. A line drawn through the body parallel to the longitudinal axis of the body may intersect more than one elongated element.
The body may comprise an elongated hollow cylinder and an insert configured to be inserted into the cylinder. The acoustic transmitter may be mounted on a ring which substantially acoustically decouples the acoustic transmitter from the tool body and the insert by one or more air gaps. The acoustic transmitter may be mounted on a ring which substantially acoustically decouples the acoustic transmitter from the tool body and the insert by one or more elastomeric contacts. The acoustic receiver may be mounted on a ring which substantially acoustically decouples the acoustic receiver from the tool body and the insert by one or more air gaps. The acoustic receiver is mounted on a ring which substantially acoustically decouples the acoustic receiver from the tool body and the insert by one or more elastomeric contacts. The acoustic transmitter may be substantially acoustically decoupled from the body by one or more air gaps and the acoustic receiver may be substantially acoustically decoupled from the body by one or more air gaps. The acoustic transmitter may be substantially acoustically decoupled from the body by one or more elastomeric contacts, and the acoustic transmitter may be substantially acoustically decoupled from the body by one or more elastomeric contacts.
The acoustic noise energy absorption element may be bonded to the receiver portion of the insert. The acoustic noise energy absorption element may be located so as to absorb acoustic noise energy traveling from the electronics portion toward the acoustic receiver.
In general, in another aspect, the invention features an acoustic logging tool comprising an elongated body having a top (first end) and a bottom (second end), an acoustic transmitter, and an acoustic receiver at a distance from the bottom (second end) of the body less than the distance from the bottom (second end) to the acoustic transmitter. The acoustic logging tool further comprises an acoustic energy absorber configured to absorb acoustic energy traveling toward the acoustic receiver from the direction of the bottom (second end) of the body.
In general, in another aspect, the invention features an acoustic energy absorption element for use in an acoustic logging tool comprising a material having an acoustic impedance between 20% and 120% of the material used to construct the acoustic logging tool.
Implementations of the invention may include one or more of the following. The material may comprise a metallic particles/bonding material compound. The metallic particles/bonding material compound may have a specific gravity between 2 and 25. The metallic particles/bonding material compound may have a specific gravity between 8 and 15. The acoustic absorption element may have an elongated shape. The acoustic absorption element may have a toroidal shape. The acoustic absorption element may have a cylindrical shape.
In general, in another aspect, the invention features an acoustic logging tool comprising an elongated body, an acoustic transmitter, an acoustic receiver, and an acoustic energy absorption element conformed to the shape of the body.
Implementations of the invention may include one or more of the following. The acoustic energy absorption element may be conformed to the shape of a cavity formed by the body. The acoustic energy absorption element may be the same size as the cavity. The acoustic energy absorption element may be larger than the cavity and may have to be compressed to fit in the cavity. A band may be configured to compress the acoustic absorption element. The band may be substantially not in contact with the body. The body may support the band if the band is struck. The band may comprise a key configured to fit in a notch in the body. The band may have a smaller diameter than the body. The band may have the same diameter as the body.
The acoustic energy absorption element may be elongated. The acoustic energy absorption element may be compressed along an axis of elongation.
In general, in another aspect, the invention features an acoustic logging tool comprising an elongated hollow tool body, an insert configured to be inserted into the tool body, and a ring configured to be inserted onto the insert. A first element is supported by the ring and exposed to a pressure field, and a second element is supported by the ring and exposed to a pressure field. The first element and the second element translate pressure from outside the tool body to the ring. The first element is supported on the opposite side of the ring from the second element, so that pressure translated to the ring by the first element substantially cancels the pressure translated to the ring by the second element.
In general, in another aspect, the invention features an acoustic logging tool comprising an elongated hollow tool body, an insert configured to be inserted onto the tool body, a ring configured to be inserted onto the insert, a first acoustic element supported by the ring, and a second acoustic element supported by the ring.
Implementations of the invention may include one or more of the following. The ring may be substantially isolated from the insert through air gaps. The ring may be substantially isolated from the insert through elastomeric elements. The first element may be a transmitter. The second element may be a transmitter. The second element may be a plug. The first element may be a receiver. The second element may be a plug. The acoustic logging tool may comprise an insert configured to be inserted into the tool body, the ring configured to fit around the insert, and the insert, tool body and ring may be positioned to have substantially no metal contact between the ring and the tool body and between the ring and the insert.
In general, in another aspect, the invention features an insert for use in an acoustic logging tool comprising a tool body, the insert being inserted in the tool body, the insert comprising a transmitter portion for supporting an acoustic transmitter, the acoustic transmitter being mounted on a ring, the ring substantially acoustically decoupling the acoustic transmitter from the insert.
An acoustic noise energy absorber may be supported by the insert. The insert may comprise an electronics portion for supporting an electronics package.
In general, in another aspect, the invention features an insert for use in an acoustic logging tool comprising a tool body, the insert being inserted in the tool body. The insert comprises a receiver portion for supporting an acoustic receiver, the acoustic receiver being mounted on a ring, the ring substantially acoustically decoupling the acoustic receiver from the insert.
Implementations of the invention may include one or more of the following. An acoustic noise energy absorber may be supported by the insert.
In general, in another aspect, the invention features a method for absorbing acoustic energy traveling through a body, the body being part of an acoustic logging tool, the method comprising conforming an acoustic energy absorption element to the body.
Implementations of the invention may include one or more of the following. The method may include compressing the acoustic energy absorption element.
In general, in another aspect, the invention features a method for acoustic logging comprising transmitting acoustic energy from an acoustic transmitter through a body. The method includes absorbing at least a portion of the acoustic energy traveling through the body in a first mode using a first absorber and absorbing at least a portion of the acoustic energy traveling through the body in a second mode using a second absorber.
In general, in another aspect, the invention features a method for acoustic logging using an acoustic logging tool comprising an elongated hollow tool body, an insert inserted into the tool body, an acoustic transmitter supported by the insert and an acoustic receiver supported by the insert. The method comprises acoustically decoupling the acoustic receiver from the insert by mounting the acoustic receiver on a receiver ring.
Implementations of the invention may include one or more of the following. The decoupling may be accomplished by one or more air gaps. The decoupling may be accomplished by elastomeric elements. The method may comprise substantially acoustically decoupling the acoustic transmitter from the insert by mounting the acoustic transmitter on a ring, the ring having one or more air gaps. The method may comprise substantially acoustically decoupling the acoustic transmitter from the insert by mounting the acoustic transmitter on a ring, the ring having one or more elastomeric elements.
In general, in another aspect, the invention features a method for acoustic logging using an acoustic logging tool comprising an elongated hollow tool body comprising a tool body material, an insert inserted into the tool body, an acoustic transmitter supported by the insert and an acoustic receiver supported by the insert. The method comprises blending metallic particles and a bonding element into a compound having acoustic impedance between 10% and 120% of the acoustic impedance of the tool body material, and conforming the blended compound to the tool body.
Implementations of the invention may include one or more of the following. Conforming may comprise conforming the blended compound to a cavity formed by the tool body. The method may comprise compressing the blended compound.
In general, in another aspect, the invention features a method for absorbing acoustic energy in a transmission medium comprising suspending particles of a first material having a first specific gravity in a matrix of a second material having a second specific gravity.
Implementations of the invention may include one or more of the following. The method may further comprise adjusting the acoustic impedance of the combined first and second material to match the acoustic impedance of the transmission medium. The absorbing material may be used to absorb acoustic energy in a logging tool. The logging tool may be an acoustic logging tool.
In general, in another aspect, the invention features an acoustic logging tool comprising an elongated body, an acoustic transmitter, an acoustic receiver, and an acoustic energy absorber supported by the body. The acoustic logging tool comprises a first absorber for absorbing flexural acoustic energy, and a second absorber for absorbing compressional acoustic energy.
Implementations of the invention may include one or more of the following. The first absorber may comprise one or more toroidal-shaped elements. The second absorber may comprise one or more elongated elements. The elongated elements are inserted into the body. Each elongated element of the second absorber may be inserted into the body tangent to an arc centered on a longitudinal axis of the body, the arc having a radius smaller than an outside diameter of the body. A projection of the elongated elements onto a plane perpendicular to a longitudinal axis of the may cover between 10 and 70 percent of the cross section of the body. A line drawn through the body parallel to the longitudinal axis of the body may intersect more than one elongated element. The first absorber may be placed substantially at the region of the body where the flexural acoustic energy is prevalent. The first absorber may be placed substantially adjacent to the transmitter. The second absorber may be placed substantially at the region of the body where the compressional acoustic energy is prevalent. The first absorber may be placed substantially adjacent to the receiver. The second absorber may be placed next to or at a distance from the first absorber and between the transmitter and the receiver. The presence of the first absorber may enhance the effectiveness of the second absorber.
In general, in another aspect, the invention features an acoustic logging tool comprising an elongated body, an acoustic transmitter, an acoustic receiver, and an acoustic energy absorber. The acoustic energy absorber comprises a first absorber for absorbing a first mode of acoustic energy, and a second absorber for absorbing a second mode of acoustic energy.